1. Field of the Invention
The present invention relates to techniques for prevention of electrical shock, and more particularly to a power breaking apparatus for protecting users against electrical shock by breaking power supplied to an electrical structure when leakage voltage occurs over predetermined voltage or the electrical structure is inundated.
2. Description of the Related Art
Generally, when there is leakage current or leakage voltage at electrical structures such as streetlights and traffic lights etc., industrial equipment used in factories and houses etc., appliances such as electric washing machines, refrigerators, etc., or such electrical structures, industrial equipment and electrical appliances are inundated by water, power supplied thereto must be cut to protect users against electrical shock.
A conventional power break apparatus capable of protecting users against electrical shock is disclosed in FIG. 1 when such streetlights and traffic lights are inundated by water. Namely, FIG. 1 illustrates the structure of the conventional ground current break apparatus. As shown in the drawing, a plurality of metal posts 100 is installed with a predetermined distance therebetween. Each of the plurality of metal posts is supported by a plurality of supporters at its lower part and has lamps (not shown) for displaying traffic lights or illuminating the street at its upper end.
Also, a controlling unit 110 for supplying AC power to the lamps of the plurality of metal posts 100 and controlling AC power thereto is separately installed from the plurality of metal posts 100.
The controlling unit 110 includes wiring breakers 111 and a magnetic switch 113 for automatically breaking AC power when a transient current occurs, power lines 115 for supplying AC power to the lamps of the plurality of metal posts 100, a zero phase current transformer (ZCT) 117 installed on the power lines 115 connected to output terminals of the magnetic switch 113 for outputting a leakage detection signal, a leakage zero phase detector 119 for controlling the wiring breakers 111 and the magnetic switch 113 to break AC power supplied to the lamps based on the leakage detection signal of the ZCT 117.
The controlling unit 110 is operated the following manner: The ZCT 117 detects a difference between currents flowing into the two power lines 115 when AC power supplied to the lamps of the plurality of metal posts 100 is leaked, and outputs the leakage detection signal indicative of leakage current. The leakage zero phase detector 119 controls the wiring breakers 111 and the magnetic switch 113 according to the leakage detection signal of the ZCT 117 such that AC power is not supplied to the lamps. Also, the wiring breaker 111 detects transient current when it flows to the lamps through the power lines 115, and then automatically breaks AC power. Therefore, the controlling unit 110 can immediately break AC power supplied to the metal post sides when there is a leak, thereby protecting users against electrical shock.
In such an electrical structure, the power lines 115 are typically laid under the ground from the controlling unit 110 to the lower part of the plurality of the metal posts 100. Meanwhile, other power lines 103, passing through space formed within each of the plurality of the metal posts, are used to connect the power lines 115 under the ground and the lamps installed at the upper end of the plurality of the metal posts. Therefore, AC power is supplied to the lamps from the wiring breakers 111 and the magnetic switch 113 through the power lines 115 and 103.
Meanwhile, in order to electrically connect the power lines 115 and the other power lines 103 to each other, there is provided a box 105 installed on a metal post 100 and located about 50 cm off the ground. Therefore, a worker can electrically connect the power lines 115 and 103 through the box and then tape the connection line parts 117 with an insulation tape. Event though the box 105 is installed about 50 cm off the ground, when the box 105 including the connection line parts 117 is inundated by flood etc., AC power may be leaked to water therefrom. Therefore, a passerby passing near the metal post from which AC power is leaked to water may be electrically shocked. Thus, the conventional controlling unit 110 includes the ZCT 117 and the leakage zero phase detector 119, which can detect a leakage of AC power and, if present, control the wiring breakers 111 and the magnetic switch 113 to break AC power supplied to the metal post side, thereby protecting the passersby against electrical shock.
However, even though the power lines supplying AC power from the controlling unit 110 to the metal posts sides 115 are typically buried under the ground to be protected from mechanical damage and to be electrically isolated from other lines or devices, they cannot be substantially electrically isolated from the external environment. Namely, there is a relatively small amount of leakage current through an insulation part of the power lines 115 regardless of inundation thereof. Therefore, if the ZCT 117 and leakage zero phase detector 119 are set to be too sensitive, they can operate the wiring breakers 111 and magnetic switch 113 to break AC power supplied to the lamps of the metal posts with respect to a relatively small leakage current flowing from the isolation part of the power lines 115 to the ground, thereby easily turning off the lamps.
To prevent such problems, the ZCT 117 and leakage zero phase detector 117 are set to operate the wiring breakers 111 and magnetic switch 113 to break AC power only if they detect a predetermined leakage current. Even though they operate based on the settings, since they allow leakage current under the predetermined leakage current, they cannot completely prevent electrical shock of passersby from the leakage current.
To solve the problem, Korean Utility Model Registration No. 255182 (Korean Utility Model Application No. 20-2001-24190) filed by the present applicant discloses an apparatus including inundation sensor rods installed within the metal posts for sensing inundation of the metal posts. Therefore, when the inundation sensor rods sense inundation of the metal posts, transient current is generated and flows through AC power by contacting contact points of the relays. Then, wiring breakers 111 of a controlling unit 110 detect the transient current to break AC power supplied to the metal post side.
However, since the apparatus of Korean Utility Model Registration No. 255182 operates such that contact means, such as a relay, for connecting AC power lines to each other to generate a short current, contact points of the contact means can be easily damaged by the short current. Therefore the conventional apparatus has disadvantages in that the contact means such as a relay, a magnetic switch, and an MCCB (Moulded Case Circuit Breaker) etc. must be frequently replaced with new ones.